A USAir DC9 with landing-gear problems broke off its landing appraoch at National Airport yesterday morning after receiving a last-minute warning from the pilot of a private plane waiting to take off.

The airliner, Flight 252 from Cincinnati to Washington with 63 passengers aboard, landed safely at Dulles International Airport on a runway coated with firm-retardant foam after circling for an hour to lighten its fuel load.

"I'm still shaking, man," said Richard Gregory, a Cincinnati restaurateur on the flight. "Any time they tell you to put your head down by the seat and brace yourself, it's scary as hell."

A federal Aviation Administration spokesman said a preliminary examination showed that a nut in the landing gear had fallen off and that a piece of equipment that ordinarily prevents the gear from moving sideways had malfunctioned.

One FAA spokesman yesterday called the situation "not a common type of thing," then added that there had been "no great danger."

Gregory, who was Washington-bound for a party last night at the Greek Embassy, said the plane was a few feet above the runway when it suddenly pulled up.

"The wheels were ready to touch. I thought when they pulled up that maybe we'd picked the wrong airport, that maybe they'd goofed up there [in the cockpit]. Everybody in the plane just sat there spellbound. They didn't know what to say."

Gregory said no announcement was made by the pilot for about five minutes. Then, as the plane prepared to land at Dulles, the passengers were instructed on emergency-landing procedures.

"They told us to take off all jewelry -- earrings, false teeth, that sort of thing. And then we had to put our heads down," he said. Gregory said when the plane landed, the passengers applauded -- "just like Las Vegas."

"Nobody even realized how serious it was until after we landed," he said. "Then I got into a cab and broke into a cold sweat."

FAA spokesman Fred Farrar said an unidentified private pilot at National radioed the DC9 after noticing the plane's left landing gear was not parallel to the others. The airline pilot aborted the landing and was directed by the National tower to fly to Dulles, which has longer runways and less traffic.

After circling to use fuel and reduce the danger of fire, the plane landed without incident at 9:33 a.m. The plane touched down first on its right wheel and then on its left, and that action snapped the landing gear into place, according to an FAA spokesman.

The entire, 6,000-foot length of the landing strip was covered with one to two inches of light gray, foul-smelling foam.

Gregory said the incident was unsettling. "When I got to the Holiday Inn [in Washington] and got into the elevator, the damned elevator doors didn't open. I had to push the alarm and make the elevator go back down to the lobby. I said, 'Man, this just ain't my Day!'"